The purpose of the pressing process is to make cakes of uniform density. This way, when the cakes are broken down into grains later, this ensures that the grains are of uniform density as well, which means that the rate of combustion will also be uniform between different batches of gunpowder. This is very important for accuracy because the gunpowder should fire with the same power, even if the powder is taken from different barrels.
After the ingredients of the powder are mixed together, it must be broken down to a meal powder before it is put into a press. This breaking down process was done in two ways: really large pieces were hit with wooden mallets to break them into smaller pieces and then the pieces were put into a “breaking-down” machine.